I recently sent kovid a set of patches which implemented a cropping tool for pdf's for the command line. It was released in yesterdays version Version 0.4.127. Basically you can use it to reduce the page by a set amount or use the output of ghostscript to automatically crop pages.

The usage is :

Code:

pdftrim --help
Usage: pdftrim.py [options] file.pdf
Crops a pdf.
Whenever you pass arguments to pdftrim.py that have spaces in them, enclose the arguments in quotation marks.
Options:
--version show program's version number and exit
-h, --help show this help message and exit
--verbose Be verbose, useful for debugging. Can be specified
multiple times for greater verbosity.
-o OUTPUT, --output=OUTPUT
Path to output file. By default a file is created in
the current directory.
-x BOTTOM_LEFT_X, --leftx=BOTTOM_LEFT_X
Number of pixels to crop from the left most x (default
is 10)
-y BOTTOM_LEFT_Y, --lefty=BOTTOM_LEFT_Y
Number of pixels to crop from the left most y (default
is 10)
-v TOP_RIGHT_X, --rightx=TOP_RIGHT_X
Number of pixels to crop from the right most x
(default is 10)
-w TOP_RIGHT_Y, --righty=TOP_RIGHT_Y
Number of pixels to crop from the right most y
(default is 10)
-b BOUNDING, --bounding=BOUNDING
A file generated by ghostscript which allows each page
to be individually cropped [gs -dSAFER -dNOPAUSE
-dBATCH -sDEVICE=bbox > bounding]

Like all of calibre it is free under the gpl. As its part of calibre its not going to get horribly complicated but I hope it will be usefull